DE102019213404A1 - Process for producing a molded part - Google Patents

Abstract

The invention relates to a method for producing a molded part (2), comprising providing a green part, in particular by means of a binder jetting process, the green part comprising green part particles according to a green part material composition with a first particle size and a binder, activating the binder to harden the binder and for producing a molding blank and sintering the molding blank to produce the molding (2). It is provided that a downstream dip coating, after the molding blank has been built up, the surface (5) of the molding blank and thus of the molding to be produced (2) or directly the surface (5) of the molded part (2) can be treated by the dip coating and specifically adapted to the requirements of the molded part (2). Dip-coating comprises dipping the molded part blank and / or the molded part (2) into a slip (4) comprising a binder and powder particles (3), the powder particles (3) having a second particle size that is smaller than the first particle size.

Description

The invention relates to a method for producing a molded part, comprising providing a green part, in particular by a binder jetting process, the green part comprising green part particles according to a green part material composition with a first particle size and a binder, activating the binder for curing the binder and for production a molded part blank and sintering the molded part blank to produce the molded part.

In a first process step, a green part is provided. For example, the green part can be produced by any additive manufacturing process. In particular, the green part can be produced by a binder jetting process. In this case, green particles, in particular made of metal, are used as the starting powder and connected in layers by means of a binder in the shape of the molded part to be manufactured, for example glued. The green particles are typically present as a powder in a powder bed. The green particles are powdered in layers and the green particles are locally solidified by the binder. The entire powder bed with the green part to be manufactured embedded in it is lowered together, with a new layer of the green part particles and possibly binder being applied. This is followed by a new layer of metal powder and, if necessary, renewed local solidification of the green particles by the binder. This process is repeated until the green part is built up. The green part material composition, that is to say the material composition of the green part, thus comprises the green part particles and the binder.

In order to be able to build up the green part effectively, the green part particles are in the form of a powder with a certain particle size. The particle size is decisive for how thick, for example, a layer can be that can be built up in one production step. The particle size also has an influence on the surface properties of the molded part to be manufactured.

The provided green part is characterized by only limited strength, since it or the green part particles from which the green part is made up is / are only held together by the applied or introduced binder. Before the green part can be removed from the powder bed, the binder is especially thermally activated and hardened (curing process), with a molding blank being created by the especially thermal activation and hardening of the binder. The molding blank is then de-powdered in order to remove excess powder adhering to the molding blank from the powder bed. The molding blank therefore has a material composition which has the green particles and in which the binder is removed, for example, by burning out, so-called thermal debinding, in particular in the sintering process that follows the curing process.

In order to produce the molded part, the molded part blank is sintered or sintered, during which the binder is burned out and the green part particles are sintered together in the shape of the molded part to be produced. The molding is produced from the molding blank by sintering. This is done with the help of heat and pressure until a target density, for example the highest possible density, is reached. During sintering, the porosity is reduced and the volume of the molded part blank decreases due to shrinkage, that is, the molded part is typically smaller than the molded part blank.

In the prior art, other methods for producing or building up molded parts are also known. For example disclosed WO 2018/086645 A1 as an additive manufacturing process, a process for the manufacture of 3D molded parts with a dip coating process.

Dip coating is carried out to apply a layer of powder. Dip coating is the process of building up the molded part and gives the molded part to be produced its geometry and outer contour. The molded part is accordingly produced starting from a building platform as follows: lowering the building platform into a suspension consisting of an aqueous solution in which particles are suspended, the building platform remains in the suspension, after a certain process time the building platform is raised. The construction platform is moved out of the immersion bath with the suspension when it is lifted and a layer of the suspension remains on the surface of the molded part to be manufactured. The layer is then scraped off with a doctor blade so that a homogeneous layer thickness results. Optionally, the layer is dried and locally solidified by means of a binder, which is optionally dried. In order to apply a new layer to the surface of the molded part to be manufactured, the building platform is again immersed in the suspension and the previous steps are repeated until the molded part is built up.

The dip coating of the molded part to be built up in the suspension serves as a method for applying a further layer through the particles suspended in the suspension instead of the powder bed in the binder jetting process. The process step of layer application by dip coating increases the complexity of the entire system and the process and increases the process time compared to the binder jetting process, especially when using fine powders or small particles suspended in the aqueous solution, in which only a small layer thickness can be achieved per application. In addition, the flow properties of the suspension are not solely dependent on the aqueous solution or the particles, but rather on the possibly complex rheology of the suspension. The effectiveness and controllability of the manufacturing process are therefore dependent on the size of the powder particles. The process is particularly complex if the powder particles are very small, since this means that many layers have to be applied in order to achieve a certain size of the molded part.

In the known manufacturing processes, there is the problem that the size of the particles or the green part particles directly determines the porosity of the green part and thus of the molded part or molded part to be manufactured and the size of the particles is at the same time decisive for the effectiveness of the structure of the green part or the molded part. The size of the particles also has an influence on the surface properties, in particular the roughness of the surface, of the molded part. When using large particles, the size of the particles means that quality standards cannot be met in some cases. The mechanical properties of the molded part depend on the green part density, i.e. the packing density of the powder particles in the green part. Typically, a compaction of the powder particles is necessary in order to achieve an adequate quality of the surface. Furthermore, during or after the surface or the uppermost layers of the molded part are polished, the powder particles are visible through insufficient pores close to the surface, which, according to current quality standards, prevent their use in series components. Too small a size of the particles reduces the effectiveness of the structure.

These problems can be reduced, for example, by treating the molded part by hot isostatic pressing after the sintering process or after sintering. However, hot isostatic pressing is very expensive. Alternatively, the green part can be infiltrated with a low-melting alloy, but the infiltration only achieves inadequate mechanical properties of the molded part and requires further mechanical process steps or subsequent treatments.

The invention is now based on the object of specifying an improved production method for the effective and functionally versatile production of a molded part with which, in particular, an improved surface quality of the molded part can be achieved.

The invention solves the problem with the features of independent claim 1.

According to the invention, it is proposed that dip-coating and sintering of the molded part blank and / or dip-coating of the molded part take place. The method enables the molded part blank or the molded part to be removed from or after the binder jetting process and coated by the dip coating in a separate step outside the system for producing the molded part blank or the molded part, i.e. in a potentially subsequent process step . The subsequent dip coating after the molding blank has been built up allows the surface of the molding blank and thus of the molding to be manufactured or directly the surface of the molding to be treated by the dip coating and specifically adapted to the requirements of the molding.

Dip coating here comprises immersing the molded part blank and / or the molded part in a slip comprising a binder and powder particles. The slip is a suspension in which the powder particles are suspended.

According to the invention, the powder particles have a second particle size which is smaller than the first particle size. The dip coating enables a redensification of areas close to the surface. For example, the slip and / or the powder particles contained therein can penetrate into pores of the molded part blank and / or the molded part near the surface and lead to an additional compaction of the surface there. This has a positive effect on the green part strength and density or the strength and density of the molded part blank or molded part and has a particularly positive effect on the sintering process. By using small grain sizes or powder particles, compaction close to the surface can be achieved in the sintered part or in the finished molded part. In particular, the surface can be completely homogeneous and is therefore particularly resistant to mechanical and chemical loads, as is required for tools by quality standards, for example.

According to the invention, the dip-coated molding blank and / or the dip-coated molding is then debindered. The binder is removed from the surface of the molded part blank or the molded part. The molded part blank is prepared for sintering.

The invention has recognized that a dip coating in which the powder particles have a second particle size which is smaller than the first particle size has advantages over that Manufacturing process of the green part as such with only one particle size, such as in the WO 2018/086645 A1 is revealed. The dip coating of the molded part blank or the molded part as a provided part to be coated, in particular by means of the binder jetting process, takes place with powder particles as a downstream process step. The surface of the built-up molded part blank or of the finished green part and / or of the molded part is treated. The surface quality can thus be improved and / or graduated in a targeted manner.

The dip coating according to the invention, i.e. applying a suspension in a downstream process step to the molded part blank or the finished and not yet sintered green part or to the molded part, taking into account the targeted use of powder particles and green part particles of different sizes, is not known in the prior art.

In a preferred embodiment of the invention it is provided that the powder particles have a diameter of up to 15 μm, preferably of up to 10 μm, more preferably of 5 μm. However, it is also possible for the powder particles to have a size in the nanometer range. The powder particles are therefore very much smaller than typically used green particles. This embodiment has recognized that the size of the powder particles mentioned is unsuitable for building up a green part or a molded part blank, since the layer thickness that can be achieved for an individual layer is only insufficiently thin, which requires a large number of repetitions for a given size of the green part or to achieve the molding blank. However, it has surprisingly been shown that advantages can be achieved in the subsequent immersion treatment. The powder particles with the second particle size in the specified range make it possible to produce a pasty slip. The pasty slip adheres particularly advantageously to the surface of the molded part blank and / or the molded part. The specified range of the size of the powder particles is particularly advantageous for the roughness and / or the porosity of the surface of the molded part to be finished. This allows the powder particles to close the pores between the green particles.

In a further preferred embodiment of the invention it is provided that the slip has powder particles which consist of a powder material comprised by the green part material composition. In this way, a materially homogeneous molded part can be produced which has a higher density, fewer or no pores, less roughness and / or greater strength on its surface than inside the molded part. As a result, a functional section can be formed on the surface of the molded part which is made of the same material as the green part particles which form the interior of the finished molded part. The functional portion of the molded part is a portion of the surface of the molded part treated by the immersion treatment, the physical and / or chemical properties of which have been improved by the immersion treatment with respect to the interior of the advantage. The slip advantageously has powder particles which consist of a powder material different from the green part material composition. Functional sections can thus be produced on the surface of the molded part which have changed or improved physical and / or chemical properties than the interior of the molded part. For example, this can improve the thermal conductivity on the surface of the molded part. In an advantageous embodiment, the slip can advantageously have powder particles made of different materials, at least one material of the powder particles being present in the composition of the green part material and at least one material of the powder particles being different from the materials of the green part. The functional sections can, for example, have functions tailored to medical technology and / or aerospace, such as being antibacterial or particularly heat-resistant.

In a preferred embodiment it is provided that the powder particles have a higher strength than the green part particles in order to be able to produce a functional section with a higher strength than in the interior of the molded part. This can be beneficial for the manufacture of tools, for example. A physical and / or chemical parameter of the powder particles can advantageously be different from that of the green particles. In particular, the physical and / or chemical parameter can be the surface roughness, the sintering activity, the porosity, the thermal conductivity, for example through use with metal powder containing copper, and / or the electrical conductivity, the manufacturing process and / or the properties of the surface to improve the molded part. The increase in the sintering activity through the use of the powder particles of the second particle size can advantageously shorten the sintering cycle. The color of the powder particles is advantageously different from the color of the green part particles in order to improve the visibility of the surface of the molded part. The use of colored metals in particular as powder particles can be advantageous, for example, in the production of decorative or decorative elements.

It is advantageously provided that the powder particles are a metal powder, carbides and / or nitrides include to produce a particularly hard surface of the molded part. The molded part is therefore suitable as a tool, for example.

The slip is preferably tempered to a predetermined temperature in order to be able to adjust the viscosity of the suspension or the slip, for example, to reduce sedimentation of the powder particles and / or to improve the adhesion of the slip to the surface of the molded part blank and / or the molded part. For homogenization, the slip can advantageously also be stirred with a stirrer, for example.

The dip coating is advantageously carried out several times in order to achieve a predetermined thickness of the surface of the molded part achieved by the dip coating. With each dip coating, a layer of a certain thickness is applied to the molded part blank or to the molded part. By repeating the dip coating, the thickness of the surface can thus be increased or reinforced until a previously defined and / or determinable thickness of the surface is reached.

In a preferred embodiment it is provided that after the dip coating, the surface of the molded part is polished in order to achieve a particularly smooth and / or pore-free surface of the molded part.

Dip-coating is preferably carried out in sections in sections of the surface of the molded part blank or of the molded part in order to provide the molded part blank or the molded part with a functional section only in certain sections of the surface. In particular, a graduated or heterogeneous molded part can thereby be produced which has different physical and / or chemical parameters in different sections of the surface of the molded part.

A drying step, a heat treatment and / or a sintering is preferably carried out after the dip coating in order to cure the binding agent present in the slip and / or to finally produce the molded part. The drying step can include, for example, a heat and / or UV treatment in order to be able to follow a further step in the aftertreatment early on. For example, the time between two dip coatings can be reduced by a drying step.

Further preferred embodiments of the invention emerge from the other features mentioned in the subclaims.

The various embodiments of the invention mentioned in this application can advantageously be combined with one another, unless stated otherwise in the individual case.

• 1 schematisch ein Formteil vor der Tauchbeschichtung;
• 2 schematisch ein Formteil in einem Schlickerbad;
• 3 schematisch ein tauchbeschichtetes Formteil;
• 4 schematisch das tauchbeschichtete Formteil gemäß 3 mit einer behandelten Oberfläche;
• 5 schematisch eine wiederholte Tauchbeschichtung eines Formteils;
• 6 schematisch ein mehrfach tauchbeschichtetes Formteil; und
• 7 schematisch das mehrfach tauchbeschichtete Formteil gemäß 6 mit einer behandelten Oberfläche.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

• 1 schematically a molded part before dip coating;
• 2 schematically a molded part in a slip bath;
• 3rd schematically a dip-coated molded part;
• 4th schematically the dip-coated molding according to 3rd with a treated surface;
• 5 schematically a repeated dip coating of a molded part;
• 6th schematically a multiple dip-coated molded part; and
• 7th schematically the multiple dip-coated molded part according to 6th with a treated surface.

1 shows schematically a molded part 2 , especially a metal part, prior to dip coating. In the embodiment shown, a green part was first provided. The green part comprises green part particles of a green part material composition with a first particle size and a binder. The green particles advantageously comprise particles made of metal. The green part can in particular be provided by a binder jetting process. The green part or the binder is then activated, for example in an oven, for example, which allows the binder to harden. The molded part blank is thus produced. The molded part is made by sintering the molded part blank 2 produced. Due to their size, the green particles are in a recognizable granular form, with cavities between the green particles 1 can form, as in 1 indicated. The molding 2 therefore typically has a certain porosity or porosity that can be determined or determined by the size of the green particles and the build-up process. The schematic representation of the cavities 1 in the figures shown corresponds to the representation of a micrograph of the molded part 2 .

In 1 is a slip bath 6th shown in the slip 4th is available. The slip 4th has, for example, an organic solution and a binder and powder particles contained therein 3rd on. The slip 4th is a suspension in which the powder particles 3rd and advantageously the binder are suspended. However, the binder can also for example in the slip 4th be resolved. For coating the surface 5 of the molded part 2 becomes the molding 2 in the slip 4th immersed as in 2 shown. The green particles can, for example, have a metallic alloy and the powder particles 3rd may have alloying elements of the metallic alloy of the green particles.

The powder particles 3rd in the slip 4th have a second particle size which is smaller than the first particle size of the green part particles. The size of the green particles and the powder particles can be determined, for example, by the mean diameter of the green particles or powder particles. The slip advantageously has 4th largely monodisperse powder particles 3rd on. The green part advantageously has largely monodisperse green part particles. However, it is also conceivable that the slip 4th different types of powder particles 3rd , for example made of different materials and / or with different sizes, with the powder particles 3rd can be polydisperse. The green particles can also be polydisperse.

2 shows schematically the molded part 2 in the mud bath 6th . The molding 2 gets into the slip over a defined period of time 4th submerged. While the molding 2 in the slip 4th is submerged, they can be in the slip 4th existing powder particles 3rd into the surface 5 of the molded part 2 penetrate and / or on the surface 5 of the molded part 2 stick. The depth with which the powder particles 3rd into the surface 5 of the molded part 2 can penetrate, in particular by adjusting the time in which the molded part 2 in the slip 4th is immersed by the temperature of the molding 2 and / or the slip 4th and / or by the size of the powder particles 3rd as well as the size of the green particles and thus the pores or cavities 1 in the molded part 2 to be influenced.

The molding 2 is then made from the slip 4th removed as in 3rd shown.

3rd shows schematically the dip-coated molding 2a . The surface 5 of the molded part 2 a layer of the slip adheres 4th and in particular a layer of powder particles 3rd at. However, the layer shown is to be understood only schematically and it is also possible that the powder particles 3rd so far into the molding 2 penetrated that the powder particles 3rd only the pores or cavities 1 seal between the green particles.

4th shows schematically the dip-coated molding 2a according to 3rd with a treated surface 5 . By treating the surface 5 will be the in the previous step on the molding 2 applied powder particles 3rd in particular cohesively with the molded part 2 connected, thereby forming a dip-coated molded part 2a is formed. Treating the surface 4th can, for example, drying the slip 4th , Curing of the binder and / or sintering of the dip-coated molded part 2a include. In one embodiment of the invention, the method for producing the molded part 2 end after the one-time dip coating. However, it is also possible, as shown in the following figures, that the dip-coated molded part 2a is repeatedly dip-coated.

5 shows schematically a repeated dip coating of a molded part 2 or a dip coating of the already dip-coated molded part 2a . The dip-coated molding 2a gets into the slip over a defined period of time 4th submerged. While the dip-coated molding 2a in the slip 4th is submerged, they can be in the slip 4th existing powder particles 3rd into the surface 5 of the dip-coated molding 2a penetrate and / or on the surface of the dip-coated molding 2a remain liable, analogously with reference to 2 explained.

6th shows schematically a molded part coated several times 2 B . The surface 5 of the dip-coated molding 2a a layer of the slip adheres 4th and in particular a layer of powder particles 3rd at. The layer applied to the molded part by the repeated dip coating 2 leads to the coating of the molded part 2 is thicker in the case of repeated dip coating than in the case of a single dip coating.

7th shows schematically the molded part which has been dip-coated several times 2 B according to 6th with a treated surface 5 . By treating the surface 5 are the in the previous step on the dip-coated molding 2a applied powder particles 3rd in particular cohesively with the dip-coated molded part 2a connected, thereby a multiple dip-coated molded part 2 B is formed.

1. 1. Herstellung eines Grünteils durch Binder-Jetting-Prozess, das heißt Pulverauftrag, lokale Verfestigung durch Binder, Aushärten des Binders, Absenken der Plattform beziehungsweise des aufzubauenden Grünteils in ein Pulverbett, Aufbringen einer neueren Pulverschicht und Wiederholung, bis das Grünteil aufgebaut ist;
2. 2. Curing beziehungsweise Aktivieren und Aushärten des Binders;
3. 3. Entpulvern der Bauteile;
4. 4. Tauchbeschichten des Grünteils mit dem Schlicker 4 beziehungsweise der Suspension, umfassend eine wässrige Komponente und feines Metallpulver mit einer Partikelgröße von beispielsweise bis 5 µm, wobei die Tauchbeschichtung außerhalb der Anlage als der Herstellung des Grünteils nachgelagerter Prozessschritt stattfinden kann;
5. 5. optional mehrmaliges Tauchbeschichten;
6. 6. optional Trocknen des Grünteils;
7. 7. Entbindern und Sintern zur Herstellung des fertigen tauchbeschichteten Formteils 2a, 2b.

In summary, an advantageous method for producing the molded part 2 can be specified by the following steps:

1. 1. Production of a green part by binder jetting process, i.e. powder application, local solidification by binder, hardening of the binder, lowering of the platform or the green part to be built into a powder bed, application of a newer powder layer and repetition until the green part is built up;
2. 2. Curing or activation and hardening of the binder;
3. 3. De-powdering of the components;
4. 4. Dip-coating the green part with the slip 4th or the suspension, comprising an aqueous component and fine metal powder with a particle size of, for example, up to 5 μm, wherein the dip coating can take place outside the system as a process step downstream of the production of the green part;
5. 5. optional multiple dip coating;
6. 6. optional drying of the green part;
7. 7. Debinding and sintering to produce the finished dip-coated molded part 2a , 2 B .

In the embodiment shown, the molded part 2 dip coated. It is also possible and possibly advantageous for the molded part blank to be dip-coated before sintering. Then can for the production of the dip-coated molding 2a , 2 B the dip-coated molding blank can be sintered. Due to the dip-coated molded part blank compacted in the area near the surface, a reduction in the process-inherent shrinkage due to the sintering process can be achieved. This improves the dimensional accuracy of the molded part to be produced 2 .

List of reference symbols

1

cavity

2

Molded part

2a

Dip-coated molded part

2 B

Multiple dip-coated molded part

3

Powder particles

4th

Slip

5

surface

6th

Slip bath

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2018/086645 A1 [0006, 0017]

Claims (10)

A method for producing a molded part (2), comprising - providing a green part, in particular by a binder jetting process, wherein the green part comprises green part particles according to a green part material composition with a first particle size and a binder, - activating the binder for curing the binder and for Production of a molded part blank, and - sintering of the molded part blank to produce the molded part (2), characterized by - dip coating and sintering of the molded part blank and / or dip coating of the molded part (2), the dip coating being the immersion of the molded part blank and / or the molded part (2) in a slip (4) comprising a binder and powder particles (3), the powder particles (3) having a second particle size which is smaller than the first particle size, and - debinding of the dip-coated molding blank and / or the dip-coated molding (2a) . Procedure according to Claim 1 , characterized in that the powder particles (3) have a diameter of up to 15 µm, preferably up to 10 µm, more preferably 5 µm. Method according to one of the preceding claims, characterized in that - the slip (4) has powder particles (3) which consist of a powder material comprised by the green part material composition, and / or - the slip (4) has powder particles (3) which consist of consist of a different powder material from the green part material composition. Method according to one of the preceding claims, characterized in that - the powder particles (3) have a higher strength than the green part particles, and / or - a physical and / or chemical parameter of the powder particles (3) is different from that of the green part particles, the physical and / or chemical parameters in particular the surface roughness, the sintering activity, the porosity, the thermal conductivity and / or the electrical conductivity, and / or - the color of the powder particles (3) is different from the color of the green particle. Method according to one of the preceding claims, characterized in that the powder particles (3) comprise a metal powder, carbides and / or nitrides. Method according to one of the preceding claims, characterized in that the slip (4) is tempered to a predetermined temperature. Method according to one of the preceding claims, characterized in that the dip coating is carried out several times. Method according to one of the preceding claims, characterized in that the surface (5) of the molded part (2) is polished after the dip-coating. Method according to one of the preceding claims, characterized in that the dip-coating takes place in sections in sections of the surface (5) of the molded part blank or of the molded part (2). Method according to one of the preceding claims, characterized in that a drying step, a heat treatment and / or a sintering takes place after the dip coating.

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